Magnetic torque transmission



Jan. Z9, 1957 R. HELMER 2,779,548

MAGNETIC TORQUE TRANSMISSION Original Filed OCT.. l, 1946 6 Sheecs-Sheell 4. Wg. 2. (PRIOR ART) nventot R OBER T H ELMER 55 EW/MWU 6%;27

(lttornegs Jan. Z9, 1957 'original Filed oct. 1, 1945 R. HELMER2,779,548

MAGNETIC TORQUE TRANSMISSION 6 Sheets-Sheet 2 GOO loo 20o soo 40o 50osoo 70o eoo soo nooo noo 20o (SUP) NWT- IN REv. PER MINUTE OUTPUT I )g 5lhwcutor ROBERT HELMER Gttornegs PRIOR ART Jan. 29, 1957 R. HELMER2,779,548

MAGNETIC IORQUE TRANSMISSION original Filed oct, I, 1946 e sheets-sheet3 lnnentor ROBERT HELMER @fw/UM,

Cttornegs Jan. 29, 1957 R. HELMER 2,779,548

MAGNETIC TORQUE TRANSMISSION Original Filed Oct. l, 1946 6 Sheets-Sheet4 RELAY To PRESS 1?- swlTcH 15'15 ez 7o 61 4 71 A V-bjl/eg 74 60 @a E 7351 52 I FTQ. 11. Fg. 12.

Jan. 29, 1957 Original Filed Oct. l, 1946 B KILOGAUSSES R, HELMER2,779,548

MAGNETIC TORQUE TRANSMISSION 6 Sheets-Sheet 5 H GAussEss Fig. 13

Summer Roer-:RT HELMER Jan. 29, 1957 R. HELMER MAGNETIC TORQUETRANSMISSION original Filed oct. 1, 194e 6 Sheets-Sheet 6 TO DRIVE MOTOR220 V. D.C.

I IO V.A.C.

nited States Patent MAGNETEC TRQUE TRANSR Robert Helmer, Great Neck,hl.. Y.,

Transmission Corporation, a corpo- This invention relates toimprovements in electric devices and more particularly to a torquetransmitter in which hysteresis is employed to effect a movement of onemember positioned in the magnetic field set up by a second movingmember, and the instant app ication is a division of the co-pendingapplication Ser. No. 700,569, iiled October 1, 1946, nov/ U. S. PatentNo. 2,603,678, dated iuly 15, 1952.

An object is to produce an electrical device in which hysteresis isutilized as a working force.

Another object is to produce an electrical device of the classdescribed, in which eddy currents are reduced to a minimum and no use ismade of them.

Another object is to reduce the heating etiect heretofore present indevices of the class described, where eddy currents are present.

Another object is to produce a device of the class described havingrotatable members, one or .vhich is subject to suicient hysteresisproduction to operate in synchronism with the other member under load,and to operate at any speed other than synchronism at a greater' load,the input speed remaining constant.

Another object is to provide a device of the class described, whereinthe driven member, when held against revolution, `delivers maximumtorque. This is particularly useful when starting under heavy load.

Another object is to provide a device of the class described, includingmeans for reducing eddy current loss to permit operation of the deviceat a heat loss proportional to the load applied to the driven member.

Another object is to provide an electrical device of the class describedhaving a ring member comprised of laminated, hardened steel having highhysteresis.

Another object is to produce an electrical device of the class describedhaving pole shoe faces in combination with a ring of hard steel so thatsaid pole shoe faces overlie substantially all of the adjacent face ofsaid ring whereby increased eiciency is obtained as more fullyhereinafter described.

Another object is to provide a magnetic torque transmission of theconstruction described, capabie of transmitting any desired small orlarge power and more particularly substantial horsepower (say horsepowerand over), and yet be of reasonable size and cost.

@ther objects and advantages will be apparent from the followingspecication in which, by way of illustration, preferred embodiments ofthe device will be disclosed. it will be understood, however, that thesedisclosures are merely illustrative and not limitative of the invention,and that details of construction can be Widely varied once the maininventive concept herein disclosed is understood. The invention istherefore that broadly defined by the appended claims.

In the accompanying drawings:

Figs. 1 and 2 are diagrammatic sectional views of a prior art machine.

Figs. 3 and 4 are diagrammatic sectional views of a machine embodyingthe invention.

ice

Fia. 5 is a cross-sectional view on the line 5', 5 of Fig. 4.

Fig. 6 is a torque diagram showing torque produced by the machines shownin Figs. l, 2 and 3, 4.

Fig. 7 is a longitudinal sectional view of a machine constituting arnodcation of that shown in Figs. 3, 4.

Fig. 8 is a sectional view on the line 8, of Fig.

Fig. 9 is a longitudinal sectional view of another mac ie constituting amodication of that shown in Figs. 3, 4.

Eig. 10 is an end view of the machine Fig. 9 applied to a dynamometer.

Fig. 11 is a longitudinal sectional View of another machine constitutinga modification of that shown in Figs. 3 and 4.

Fig. 12 is a longitudinal sectional View of another machine constitutinga modification of that shown in Figs. 3 and 4.

Fig. 13 is a hysteresis curve illustrating the method of selecting steelfor use in any of the machines embodythe invention herein disclosed.

Fig. 14 is a diagram of a control system for maintaining a constantspeed of the output shaft of a machine as shown in Fig. 9 under varyingloads.

Fig. 15 is a sectional view of the worm gear potentiometer in thecontrol system Fig. 14.

Fig. 16 is a diagram of a control system for maintaining a constant H.P. output from a machine such as that shown in Figs. 7 and 8.

Fig. 17 is a diagram of a control system for maintaina constant let-orftension on a roll of paper or the like, utilizing the machine shown inll.

Before describing physical embodiments of the invention, it is desirableto point out t at in all electrical rotating machines there are what arecor .only called core losses. rhis term core loss is employed todesignate the total internal loss in the rotating apparatus dueto thecombined effect of eddy currents and hysteresis. But, as the losses dueto the former are governed by laws totally diiferent from thoseapplicable to the latter, special analysis is required to distinguishone from the other.

.Eddy currents Since a varying magnetic field induces an E. M. F. inevery path that links the flux, such an E. ivi. F. will, in general,cause a flow of current in the magnetic materials comprising themagnetic circuit. Such cur ents, called eddy currents, or Foucaultcurrents cause i losses.

if the mass of iron in an armature pole is so disposed that, as itrotates, the distribution of the lines of force in the narrow field (airgap) between the armature and pole piece is being continually altered,then, even though the total amount of magnetism of tl e field remainsunchanged, eddy currents Wiil be set up in the pole piece, causing heatwhich performs no useful v/orlr.

The eddy current loss, per cycle, is directly proportional to thefrequency and the total eddy current loss is proportional to the squareof the frequency. In electrical machinery these eddy currents are oftenresponsible for more than 50% of the total core losses.

The energy generated by eddy currents is dissipated in heating the iron.rl`he paths of the eddy currents are more or less indeterminate, beingin general dependent upon the shape of the iron with respect to thedirection of the linx.

Hystei'csis Hysteresis is that quality in iron which causes the causes aloss when the direction of induction is reversed and results in theheating of the iron. It increases in direct proportion to the number ofreversals, and approximately as the 1.6th power of the maximum value ofthe induction in the iron.

In a motor, when the iron pole pieces of an armature are caused torotate-past stationary eld poles, hysteresis results and appears as acounter-torque. That is, a torque counter to the direction of therotation of the armature. This counter-torque is produced by theunwillingness, so to speak, of the iron molecules to be continuallyorientated and re-orientated, and is used in carrying out the inventionherein disclosed. v

The established practice to minimizehysteresis loss is to select a softiron or steel with the highest permeability. An iron with a high B/Hcurve or a high permeability has a very small retentivity and coerciveforce, therefore the molecular friction is small. In-prior -art deviceswhere steel is mentioned, it usually has characteristics that willreduce hysteresis to a minimum as the hysteresis is not used to performuseful work. l

The area `of a hysteresis loop is proportional to the hysteresis loss.It is shown that thin lasninations have higher hysteresis losses perunit weight than thick sheets, and the liner the grain structure, thegreater the hysteresis loss.

The hysteresis loss per cycle is independent of the frequency; i. e. thetotal hysteresis loss is directly proportional to the frequency.

Magnetic analysis of iron show that there is a relation betweenmechanical and magnetic properties. There is a very striking relationbetween hysteresis and mechanical properties, such as hardness andtensile strength. By plotting Brinell hardness and the tensile strengthagainst the product of the maximum induction and coercive force (BmXHc),this product is found to be approximately proportional to the hysteresisloss.

The magnetic properties of a material are often greatly affected by heattreatment. A quench produces mechanical strains in the material which,in general, lowers the magnetic quality by causing a decrease in thepermeability and an increase in the coercive force and the hysteresisloss. It increases HC. Y

Bearing the foregoing relationship in mind, the inventive concept hereindisclosed is that of reducing eddy currents to a minimum, while at thesame time provision is made to increase hysteresis to a maximum. This,in any given device may be attained by selecting a suitable steel, suchas a high carbon steel and hardening it, and using it in the form ofthin laminations of fine grain structure, these forming a magneticcircuit with the highest hysteresis possible. By this means it ispossible to make use of the hysteresis (heretofore a loss) as a means oftransmitting torque from one member to another while reducing eddycurrent losses to a minimum.

It will be observed that former practice has been deliberately avoidedin the constructions to be presently described herein, the inventionutilizing magnetic phenomena (hysteresis) in a new and useful way.

By way of illustra-tion, the invention will be applied to a magnetictorque transmission, although it will be obvious that it can be appliedto many other electrical devices used for a wide variety of purposes.

In such torque transmissions, there is a driving member usuallyconnected to a source of power such as an electric motor, and a drivenmember connected to the work, for example, a printing press or the like.

The driving and driven members are mounted to rotate one within theother in the transmissions herein described. The driving member islocated inside the driven member and carries the field windings and thedriven member is ring-shaped. It will be obvious that the position ofthe driving and driven members may be reversed from the positionherein-described, in that the driving member may be a body of steelrevolving within the driven member, which would then be the externalmember of the pair carrying theneld windings.

Prior art devices Reference will now be made to some prior art devicesas some of these have parts that pictorially resemble parts used in theinstant invention although none of -them ernbody the inventive conceptdisclosed.

These devices often comprise magnetic couplings and include a rcvolvable2 pole electromagnet, the poles of which are spaced adjacent arevolvable 2 pole permanent magnet. Usually the electromagnet is thedriving member and the permanent magnet is the driven member, and theload is connected to the driven member.

In some cases, both the driving member and the driven members arepermanent magnets.

Such magnetic couplings have been used 4in connection with driving fans,particularly cooling fans in refrigeration units for household use,where a small amount of coupling torque is necessary. l

While it is true that the permanent magnets in such devices are made ofhard steel and have high hysteresis, it will at once be apparent thatwith such devices the driving and driven members must be in step withcac-h other, as the operation of such devices is dependent upon thedirect magnetic pull of the poles of the driving member on the unlikepoles of the -driven member, and therefore the driving and drivenmembers must be in synchronism; if a-t any time the load is sufficientto cause slip, the driven member will no longer be subject to suflicientmagnetic attraction. This is the same phenomena as that which occurs ina synchronous motor when overloaded.

These `devices are usable only when a small amount of power (usuallyless than 1/20 horsepower) is to be transmitted, and are limited tosuch'fractional horsepower uses, because if any attempt is made toincrease the size or the strength of the permanent magnets to handlegreater loads, the size and cost of the device becomes prohibitive.

As an example, .it might be pointed out that a magnetic transmission ofthis type capable of handling 5 horsepower would be several times thesize and weight of an ordinary 5 horsepower motor, with which it wouldbe used, and could only run in sychronism as previously referred to.

So that, while it will be seen that devices such as described doincorporate a magnetic driven member of hard steel, they do not 'operateon the principle herein dis-closed, and do not have the advantages ofthe present invention; and cannot be used for the same purpose.

A second class of prior art machine to which reference will now be madeare termed eddy current machines. The construction of these machinespictorially resembles the instant invention, which, however, clearlydistinguish therefrom in many respects as hereinafter pointed out.

In order that these distinctions between the instant invention and theprior art may be clearly understood, reference is now made to Figs. land 2, which show diagrammatically elevational longitudinal sectionalviews of an eddy current transmission of a wel-l known type.

Referring to Fig. 1, the numeral 20 denotes the driving member of thedevice supported on the shaft 21, connected to a source of power such.as an electric motor or the like (not shown).

The driving member may have any equal number of poles N, S, and, for thesake of illustration, a standard 6 pole arrangement is shown. Thedriving member is usually constructed of iron.

Each pole has a ield winding (not shown) and the windings are connectedto a suitable source of direct current in any known manner so that thedriving member may be energized while rotating to have alternate N, Spoles as shown.

A driven member 22 is comprised of a ring of magnetic arras-ts 5material, such as iron or steel, having suciently low electricresistance to the flow of eddy currents to enable same to be set up byiiux generated in the driving member.

The driven member is supported to rotate about the path of travel of thedriving member Ztl, and a small air gap exists between th driving memberand the inner surface 23 of the driven member hereinafter sometimestermed the ring.

It will be understood that the ring is suitably supported on a spiderwhich has a shaft (not shown) axially aligned with the driving shaft 2l.

Assuming the driving member to be energized, and rotating in a clockwisedirection, and that the driving and driven members are lined up so thatthe points and 25 thereon are in line with the vertical axis 26 of themachine as shown in Fig. l, induced currents will be set up in the ring232, and may be assumed to flow in planes perpendicular to the plane ofthe paper on which the drawings aA pear. rthe currents shown at Z7 liowaway from the observer and the currents shown at 2S flow to Wards theobserver.

These induced currents arc caused by the flux indicated at 25? vv'liicnliows through the body of the ring from the poles N, S of the drivingmember.

Assuming the driving and driven members rotate so points and thereonmove from the positions shown in g. l to tnose shown in Fig. 2, it willbe apparent that the aux lines 29, are dragged through the body ot thcring as the poles N, S, rotate. Phis shifts paths 37, of the inducedcurrents in the body of the ring, thus givin.U rise to eddy currentswhich act to couple the ring to the driving member Ztl so that a torqueis generate between the members.

The torque (twisting effort) in toot pounds being Vt will immediately benoted that the face of the pole feces N, (i in devices of this kind donot substantially cove` the inner face of the ring, comparatively widegaps such as being therebetween. in fact, the poles are often tapered toincrease these gaps to cause a greater change in nur: distribution toproduce higher eddy currents. These eddy currents are induced by thesweeping of successive electromagnetic poles past given points on thering in which the eddy currents are induced, due to relative movement ofthe poles and the ring, which must occur to produce these ctnrents andany torque.

t will also be observed that it any hysteresis is present in thestructure shown Figs. l and 2, that it is parasitic o tar as anycoupling (torque) effect is concerned, being opposed to, and tending tonullity the eddy current etlect. This will be evident from a discussionof the hysteresis phenomena to be preentl'/ n resented in connectionwith uw 4 ...s improved device formi g the subject matter of thisapplication.

rEhe device shown in Figs. l nd 2 is readily recognized as adac' .t' ofa. squirrel cage noter in -which both Rotor corresnonding to 23d, Figs.l and 2, and the rel cage motor, cage bars (usually of copw i .c in theframe and 'the rotation of t .e motor rev primary magnetic iield.machine shown in Figs. l and 2, the principle saine, but the eddycurrents in the not have the directed low resistance circulationprovided bv the squirrel cage bars Jiust referred to. The eddy currentscirculate in the body of the ring Z2.

it evident therefore, that when steel is used in the ring of the eddycurrent devices shown in Figs. l and 2, that this steel is of suchcharacteristics as to form a low resistance path for the induced eddycurrents, and that this steel cannot therefore be of the samecharacteristics as lil) the steel used in the device'hereinafterdisclosed and forrning the subject matter of this application.

An analysis of the device shown in Figs. l and 2 will immediately revealthat the torque will increase with the output speed up to some givenpoint depending on the structural details ot the machine, but thatthereafter the torque will drop ott. In other Words, as the sweep rateof the poles increases above a predetermined rate, the torquediminishes.

lt will also be noted that in a machine of this descripthe driving anddriven members can never run in sync` rcnisrn, slip being present andnecessary under any conc. on ot load to provide torque.

The loss due to slip is evidenced in the formation of heat due to theeddy currents produced in such machines. if losses do not occur in theimproved device to be itly described.

art device being discussed, if the full load trie A. C. driving motor isi760 P. N., and the l). ivi., the output sneed at normal load Will be 7Ivi., the clutch slip being slightly less than 3%. n th case of a fullload motor speed of M50 R. P. ivi., ie in terms of motor sneed l -i.5%the output would f. rines s,

an n y chewn in connection with three i s e member Ztl, but vih beunderstood that they exist :nnecticn with all the poles or said member.

ft'scriprion of embodiments of .the instant invention Figs. 3 and showdiagrarnniatically, elevational longitudinal views of a torquetransmission embodying the invention. Ti'rese views correspond to viewsor" the prior art machine shovvn in Figs. l and 2.

1reterring to 3, the numeral denotes the driving member of the devicesupported on the shaft 33 connected to a source ci power such as anelectric motor or the like (not shown).

The driving member N, S, and for the salle arrangement is shown.constructed of soft iron.

Each pole has a eld winding (not shown), and the windings are connectedto a suitable source of direct current in any known manner such as thathere iter shown and described in connection with other embodiments ofthe invention, so that the driving member is energized While rotating tohave alternate N, S poles as shown.

Each pole has a pole shoe 32u. HThese pole shoe extend circurnfrentially round the path of travel or" the driving member' and the tipssuch 3d, 3S of adjacent pole shoes are close togetner so that the gap Sebetween adjacent pole shoes is reduced to a minimum.

ly providing pole sh es that cover substantially the inner face of thedriven member or ring mi', to be presently described, it will be seenthat have equal number of poles pole shoes 32p and 37, and thrw .vl enrelative motion place between the pole shoes and the ring, maximum hystcduced in the ring which would not occur it large gaps were employed atThus, considerable increase in efficiency is obta, n ot the arrangementof the pole shoes as described.

The ring 3'? is made up of a plurality of laminations of suitable steelas deiined later herein. The pianes ot the laminations extendtransversely across tie path of 'the eddy currents, as shown in Fig. 5,in order tc prevent any llov-J of eddy currents and these currents aretherefore negligible, if they exist at all, and play no part in theoperation of the device.

The ydriven member or ring 37 is suitably supported on a spider or thelike, which has a shaft (not shown) which is axially aligned with thedriven shaft 33.

Assuming the driving member 32 to be energized and rotating in aclockwise direction, and that the driving and driven members are linedup so that the points 39 and 40 thereon are in line with vertical line26 as shown in Fig. 3, flux lines will extend from the N to S poles ofthe driving member via ring 37. Sets of such lines are indicated at 41and 42.

Assuming that the driving and driven members rotate so that the points39 and 40 move from the position as shown in Fig. 3 to that shown inFig. 4, it will be apparent that the direction of the ilux lines 41-42wilt be reversed as shown at 43-44 in Fig. 4. This shift in thedirection ot' the flux lines causes hysteresis in the ring 37, whichappears as a driving torque; that is, a torque in the direction ofrotation of the driving member 32. This torque is produced by theunwillingness, so to speak, of the iron molecules in the ring 37 to becontinually orientated and reorientated. The result is that the ring 37tends to rotate along with the driving member 32.

Since the magnetic induction of the selected steel is low, being equalto the permeability U times the magnetizing force H, and consequentlyhaving a high reluctance, the shape of the pole shoes 32p is such as toincrease the magnetic induction and decrease the reluctance as much aspossible. As shown in Figs. 3 and 4, the pole shoes 33 overlie almostthe entire inner circumference of the ring 37, and the pole shoe gaps 36are relatively small. The reason fortbis has already been pointed out,but may be amplied by stating that the induction is equal to the numberof perpendicular lines of force per unit area of cross Section o fmagnetized material. Thus, the shoes 33p are made as long as possible sothat the area of the ring 37 opposite the shoes is as great as possible,making the greatest number of lines of force perpendicular to the ux.This also reduced the reluctance.

it will be observed that if any eddy currents are present in thestructure shown in Figs. 3 and 4, that they are parasitic and do notproduce any torque.

lt will also be observed that if the driving member 32 is rotated, ring37 will also rotate in synchronisrn therewith. This synchronouscondition will be maintained even if force is applied to the shaft ofthe ring 37 in a direction counter to the direction to the rotationprovided that this force (dynes) be of smaller magnitude than the workwhich would be required (in dynes) to reorient the molecules of iron inthe ring 37.

As a further example, assume the driven member 32 to be coupled to aprime mover whose speed is 1800 revolutions per minute and with acertain excitation; assume a load to be applied to the shaft of ring 37,and it slowed to a speed of 1620 R. P. M. or 90% of the speed of themember 32. Assume the device had 6 poles as shown in Figs. 3 and 4. Theneach of the poles in the rotor would cause the molecules of iron in thering 37 to be oriented and reoriented 6 times for each revolution, andsince the ring is going 180 revolutions slower than the rotor, the linesof force in the ring 37 would go through 6,480 magnetic cycles. Thiscyclic change required work to be done, and this work was caused by theload applied to the shaft of the ring 37 to slow it to 90% of the speedof member 32. The reason the ring :decelerates to the speed of 1620 R.P. M., is because at that speed the hysteresis loss in the ring inWatts, or other unit of Work is equal to the applied load in the sameunits. ln other words, the hysteresis loss is in equilibrium with theload.

Further, suppose a large load were applied to the ring shaft, such thatthe ring 37 now ran at 900 R. P. M., then the lines of force in the ringwould have gone through 36 900, or 32,400 magnetic cycles. Thehysteresis loss being proportional to frequency, or speed, would be fivetimes greater than in the above example. Stated differently, at a ringspeed of 900 R. P. M., the D. C. excitation being the same, the outputtorque would be five times greaterV than it wasat 180 R. P. M.

If a still larger load be applied to the ring shaft so that the ringslowed to 10% ofthe rotor speed, or 180 R. P. M., then the induction inthe ring would have gone through 1630 36, or 58,320 magnetic cycles, andin this case the hysteresis loss would be nine times greater.

It is seen that in this device the torque transmitting capacityincreases as the output speed decreases, and were it possible to selecta steel with an ideal hysteresis loop, the torque increase would bedoubled as the speed was halved, thereby producing a constanthorse-power output. However, since it is impossible to obtain a steelwith these ideal charatceristics, the same desired result, namely aconstant H. P. is readily accomplished by the simple expedient ofautomatically varying the excitation current with ring speed.

With this hysteresis torque transmission, an electric motor, gasolineengine or other suitable prime mover may be operated at its normalspeed, producing its maximum rate of H. P. The prime mover would then becoupled directly to the driving member 32 of the transmission and thering 37 of the transmission connected to the load. If the prime moverwere an induction motor running at 1750 R. P. M., and if the load weresuch that it required 10 H. P. at 175 R. P. M., and coils ofthe rotorwere energized to a point where the shaft of the ring member 37 wereturned with this load at 175 revolutions per minute, then the torquedelivered to the load would be 300 foot pounds, which, at this speed,would produce 10 H. P.

It is seen from the above, that, with this invention, a prime mover canbe operated at its ideal working speed and the maximum amount of torquewill be developed in the transmission to take the load from a state ofrest and gradually accelerate it to run at any desired speed.

A commercial form of the device shown diagrammatically in Figs. 3 and 4,and capable of transmitting several horsepower, has approximately thefollowing dimensions, from which the savings in space and weight madepossible by this invention can be compared with prior art devices.

Overall length 16 Overall Width 20" Area of shafts 11/2" Dimension ofring 37 as shown in cross section in Fig. 5

O. D. 19 I. D. 17; thickness-3 Number of pole pieces- 8 Approximatedimensions of each coil on a pole piece 4" x 5" x 3 long Number of turnsin each coil 1386 Resistance 10.5 ohms per coil Width of air gap 38-.0l0

Width ofgaps 36-1'.

The ux lines 41 and 42 are only shown in connection with three of thepoles of member 32 in Figs. 3 and 4, but it will be understood that theyalso exist in connection will all the poles of said member in a mannerthat will be obvious. It will be observed that the path of the ux linessuch as 41, 42 lies entirely within the steel ring 37 which is of suchproportions as those given above to have a magnetic reluctance equal orless than the magnetic reluctance of the magnetizing circuit, such asany pair of pole pieces connected by ux lines 41, Figures 3 and 4.

It will be understood that the dotted lines 41, 42, Figure 4, do notrepresent the path of the tlux but are merely lead lines to indicate theilux lines Within the steel ring 37 and how the latter shift during theoperation of the device.

Fig. 6 shows torque curves produced by two machines having the samenumber of poles and the same number of ampere turns, and constructed asnear alike as possible. The curve P is produced by the eddy currentprior art machine as described in connection with Figs. 1 and Z hereof,and curve N is produced by the improved deavvenire 9 vice employinghysteresis as described in connection with Figs. 3 and 4 hereof.

By comparing these two curves it becomes apparent that in the prior artmachine the torque decreases as the difference is speed (slip) betweenthe input and output increases, and that with applicants machine thetorque increases as the difference in the speed between the input outputincreases.

A further study of Fig. 6 will reveal that the prior art machine cannever operate at synchronism as it would produce no torque, whereasapplicants machine operating at synchronism would deliver a torque ofapproximately 9) foot pounds. In other words, applicants machine ruimingat synchronism will produce more torque than the prior art machine atits maximum.

Fig. 6 also reveals that at a slip speed of 120D, the prior art machinedelivers approximately 20 F. P., while applicants machine produces over550 F. P. torque.

Fig. 7 is a longitudinal, sectional View of a machine embodying thefeatures disclosed in Figs. 3 and 5, and shows at 45 a frame in whichdriving shaft 33 is mounted in suitable bearings to rotatably supportthe driving member and its exciting coils 53 therein. One of thebearings for the shaft 33 (such as 46) is supported in the spider orframework 47 carrying the driven member or laminated ring 3'7. This ringand its spider framework are supported in a bearing in the frame 45',and the spider is connected to a shaft t9 which is the driven shaft ofthe transmission t and is illustrative of a shaft for the ring 37 ofFigs. 3 and 4, where this shaft is omitted). The opposite end of thespider is supported in the bearing d on the shaft Mounted to rotatewith, but insulated from shaft 33, are the conductiny rings 5l, 52,which are in turn connected by suitable conductors extending throughshaft 33 to the coils of the driving member. These rings have the usualcontact brushes which are connected by conductors 5d to a source ofdirect current.

Spaced around the outer periphery of the ring 37 are the bralie coilsSS, suitably supported on the frame 45 and these coils are connected byconductors 56 to a suitable source of current via a control apparatus tobe presently described.

As shown in Figs. 9 and l0, the brake coils 55 can be omitted when notrequired. For example, when the device is used as a dynamometer whereinthe output shaft 49 is connected to a dynamometer arm 57 resting uponthe platform 5d of the scale 59.

Referring to Fig. 10, if the shaft tate clockwise under torque developedbetween the ring 37 and the member 32, the scale 59 will measure thistorque which measurement will be a measure of the power applied to thedriving shaft 33 of member 32. v

The device in `Eig. 9 may also be used as described in connection withFig. 14.

ln Fig. 1l is shown a simplified form of the device described inconnection with Figs. 3 and 4 and 7-9 inclusive. Said Fig. ll disclosesa device employingr the improved torque transmitter for applying aconstant let-olf tension on a roll of paper as it is being printed on aprinting press.

ln this embodiment of the invention, a rotatable member ell,corresponding in constructional details with the driving member 32previously described, is provided with exciting coils which areconnected via the rings 51 and 52 with a suitable control system (viawires 61 and 62) to be presently described in connection with lFig. 17.

The framework 63 has mounted thereon a stationary ring member da whichmay be in all respects (except for its mounting) constructed the same asthe driven member 37 described in connection with Figs. 4 and 5.

lt will be observed that the ring member 64 in Fig. ll is stationary atall times, and that the shaft 65 carrying the rotatable member 60 issupported in suitable bearings in the framework and revolves therein.

49 is tending to ro- Fig. l2 illustrates diagrammatically anotherembodiment of the invention as applied to a universal joint coupling andvariable speed device. Here the driving shaft 66 supports bearing 67 forthe inner ends of the shafts 66, 63. It will be observed that bearing 67merely forms a support for the ends of the shafts 66, 63u-, and does nottransmit any torque. lt is constructed to permit shaft 68 to be drivenout of line with shaft 66.

A driven member 69 is supported on the shaft 65 and rotates therewith.The construction of this member 69 may be the same as the member 33described in connection with the preceding figures. Details of themounting of the rings necessary to supply current to the windings ofmember 69 will be observed from the preceding gures and are omitted fromFig. l2.

A ring '76 of laminations constructed substantially the same as the ring37 shown in Figs. 3, 4 and 5 is supported in a spider or framework 71,mounted to rotate with shaft 6d. rlhis ring therefore constitutes thedriven member of the transmission.

It will be noted however, that either of the shafts 66 or 6d may be thedriving shaft or that the position of members 6% and '70 may 'oereversed without affecting the operation of the device. Bearings forshafts 66, 63 may be applied thereto and are not shown in Fig. l2.

1Erom what has been said respecting the torque-relationship of thedriving and driven members in Figs. 3 and 4, it will be evident how thedevice shown in Fig. 12 operates with the shafts 66, 68 out of axialalignment, as the opposed faces '72, 73 on these members are of arcuateformation to permit them to move radially about the center 7d of thebearing 67.

Steel to be used in practicing this invention The foregoing examples ofconstruction as shown in Figs. 3-5 and 7-12 inclusive are merelyillustrative of different embodiments of the inventive concept hereindisclosed, but it will be observed that all of these embodiments includea laminated steel ring such as that shown at 37, Figs. 3-5.

As has been previously pointed out herein, while prior art devices havehad rotating parts of steel such as permanent magnets and the like, andwhereas in connection with eddy current transmission the word steel hassometimes been used, to describe material used in one of the members inthe transmission, it will be apparent from the foregoing description ofthe prior art devices, that, particularly in the case of the eddycurrent transmissions, steel, when used, did not have thecharacteristics necessary to produce maximum hysteresis.

Now, referring to Fig. 13, wherein is shown a typical hysteresis curvefor a suitable steel at S and a curve for soft iron at l, it may be saidin general, that a steel with which to practice this invention should beselected in which the area of the hysteresis loop is as great aspossible. This is attained by increasing the carbon content of the steelor by the addition of sulphur, or both. some steels the carbon contentmay be brought up to 1.5%. Another factor is the heattreatment-tempering, etc., given the steel.

It is not desirable to use silicon steel which has low hysteresis. Suchsteel is very much like ingot iron, as far as hysteresis is concerned.ln fact, it may be stated that the steels used to practice the inventionherein disclosed, have characteristics which are the reverse of thesteels commonly used in the construction of prior art devices. A

As an example of a suitable steel that may be used in the constructionof a device as herein disclosed, reference is made to S. A. E. steelnumber 1040, having characteristics as defined in the Society ofAutomotive Engineers Handbook, 1946 edition, which also gives thenecessary data renormalizing, annealing, hardening, temper ing, etc.This is a medium carbon steel possessing fair .manner that will beobvious.

11 machining properties, and having deep hardening characteristics, Vandis readily obtainable commercially. It may be hardened at 1525-1575 F.in oil or water to the desired hardness.

With machines of higher capacity it might be advisable to have a cobaltsteel corresponding to FezCo with 34.5

cobalt.

It will be understood that the exact steel used for a machine of anygiven dimensions will depend somewhat on machine dimensions, taking intoconsideration the problem of machining (punching or the like), but thatsatisfactory results will be obtained if the general rule applied toFig. 13 be followed, namely, select a steel that can be machined andheat treated to the extent desired to have a hysteresis loop of maximumarea.

The nearer the curve approaches the curve I, Fig. 6, the less suitablethe material will be for practicing this invention.

Control? systems for the embodiments of the invention herein disclosedFig. 14 is a diagram of a control circuit for maintaining a constantoutput speed for shaft 49 of the transmission shown in Fig. 9. In Fig.14 the numeral 75 denotes diagrammatically a self contained gear pump;76 is a by-pass valve; 77 is an oil reservoir, '78 a sylphon bellows orother member adapted to expand and contract, depending upon the pressureof the operating liquid; 79 generally indicates a contact assemblyhaving a movable arm 8@ connected to the sylphon bellows.

A reversible motor is shown at 31 driving a worm and gear assembly 82,which operates the movable arm of the potentiometer 33, which has acontrol knob S4. The potentiometer is connected to a source of D. C. asshown. A switch 85 is connected between the A. C. current supply and themotor 81 as shown.

The apparatus is connected up in a manner that will be obvious from thediagram and in operation control knob 34 is adjusted to supply theproper current from the D. C. current supply to excite the magnet coils53 of the driving member 32, which, as has been previously described,produces a hysteresis condition in the driven member 37 to cause theoutput shaft 49 of the transmission connected thereto, to run at thedesired speed under load. The by-pass valve 76 is now adjusted so thatwhen the shaft 49 is running at the desired speed, the gear pump 75 willsupply enough oil pressure to the sylphon bellow 78 to distend the sameabout half its length. The surplus oil in the system returns to thereservoir 77 in a The movable contact 86, carried by the arm 80,connected to the bellows, is now adjusted so that it will be mid-waybetween the contacts F and S of the contact assembly 79.

Switch 85 is now closed. Now, if the load on the output shaft 49 isincreased, the speed of said shaft will decrease, and consequently thegear pump 75 connected thereto will supply less oil pressure to thebellows 7S, which in turn will operate arm 80 and cause the contact 86thereon to make contact with the contact S of the contact assembly 79.This closes the circuit through motor 81, and said motor operates tomove the arm of the potentiometer 83 in a direction that will increasethe D. C. exciting current flowing through the potentiometer 83 to thecoils 53 of the transmission. This increases the hysteresis in thedriven member 37 and consequently increases the torque thereof tobalance the increased load at the desired speed. When this balancedcondition is obtained, the bellows 78 again operates to move the contact86 into a neutral position as shown, and motor 81 ceases to operate. i

If the load of the shaft 49 is reduced, then the bellows 7S is expanded,contact 86 operated thereby will engage contact F of the contactassembly 79, and the motor 81 will operate in the opposite direction tothat just described to move the potentiometer 83 to reduce theexcitation -obtained are the reverse of those described in connectionwith the application of an increased load.

Fig. 15 is a sectional view of the worm gear potentiometer 83, Fig. 14,and in Fig. 15 a control knob 84 is rigidly secured to a shaft 87. Theworm gear assembly 82 is loosely mounted about this shaft, and ispressed against a collar 88 thereon by means of a flange and springshown at 89, in such a manner that any motion imparted to the worm gearwill be imparted to shaft S7 through the frictional engagement of theange and gear. This permits the potentiometer to be controlled by handthrough the control knob 84, or controlled automatically through theworm and gear 32. it will be understood that the moving contact 90 ofthe potentiometer is rigidly secured to the shaft 87.

In Fig. 16 is shown a control circuit for maintaining a constanthorsepower output from the device shown in Figs. 7 and 8, and isparticularly useful when applying such a transmission device to therewind of a printing press or the like. In Fig. 16, the numeral 75indicates a gear pump; 76 a by-pass valve; 91 a speed range valve; 77 anoil reservoir; '78 a sylphon bellows. Numeral 92 is a toothed rackadapted to be moved by the operation of said bellows and engaging apinion 93 which is secured to the movable arm 9() of the potentiometer94. Numeral 97 is a rheostat and 9% is a relay having an armatureContact A and fixed contacts B and R. Numeral 99 indicates a switchhaving an arm which engages the paper web 100, said switch being heldopen when the web is in proper position, and said switch being closed ifthe Web should break.

In a web printing press, the web after being printed is rewound on acore about 3 or 4 inches in diameter. It is necessary that the web inbeing rewound, should always having the same tension in order tomaintain register between successive colors applied to the web inprinting thereon. If the press were run to move the web at the rate of500 lineal feet per minute, and the rewind core had a circumference of12 inches, then the rewind shaft 49 which drives the web core shouldrotate 500 R. P. M. Now, as the diameter of the rewind core builds up asthe web is wound thereon, say to a circumference of 24-inches, the shaft49 should run at only 250 R. P. M., etc.

The ratio between the core diameter and full roll diameter is often 10to 1 or better, so that in the above case, if the circumference of theroll is increased to then-the speed of rotation would be 50 R. P. M.

In order to maintain a. constant tension on the web, it becomes obviousthat if the speed of the rewind shaft is halved, the torque appliedthereto must double to give the same web tension. To have the torquedouble as the speed halves is a necessary condition to obtain constanthorsepower.

Referring to Fig. 16, and the application of the invention to a rewind,the first step is to thread the web through a printing press and securethe end of the web 10i) to the winding core on shaft 49. rIhis bringsthe web against the arm of switch 99 which is in consequence opened.

The prime mover, such as a motor (not shown) being connected to thedriving shaft 33 of the torque transmitter, switch 101 is closed, thusenergizing the coils 55 of the torque transmitter in the previouslydescribed inanner.

The relay 96 is not energized, and consequently the armature A isresting against contact S thereof, thus supplying the coils 53 with aminimum amount of current through rheostat 95, thus producing a smalltension in the web.

When the press starting switch (not shown) is operated, relay 96 isenergized and armature contact A thereof completes the circuit throughcontact R thereof. This immediately, by reason of the position of therheostat arm 90, permits a maximum current to iow to the coils 53, whichaccordingly produce hysteresis in the driven member 37 of thetransmission as previously described, which accelerates the shaft 49. Asthis shaft increases in speed, the gear pump 75 supplies (with valve 76in proper setting) sufcient oil to the bellows 78 to cause rack 92 andgear 93 to move the contact arm 90 of the potentiometer 94 to furnishthe precise amount of current necessary for the coils 53 to createsuicient torque at the desired speed.

As the diameter of the rewind roll of paper 100 increases, and the shaft49 as a result begins to rotate slower, the gear pump 75 supplies alesser amount of oil to the bellows 78, and as the bellows contracts, itmoves the rack and pinion 92 and 93 to move the contact arm 90 of thepotentiometer 94 to gradually increase the excitation of coils 53,thereby increasing the torque in the transmission proportionally to thereduction in speed of shaft 49.

If the web should break, the arm of switch 99 resting thereon, will moveto open the switch, which opens the circuit through relay 98, contactarm A of which then makes contact at B. This completes a circuit fromthe D. C. sources through the brake coils 55, which magnetically breakthe rotation of the driven member 37 of the transmission, therebystopping the web.

A. rheostat 97 is included in the circuit as shown, for the purpose ofsetting up a predetermined tension on the web required for differenttypes of material such as paper board, paper, cellophane, etc.,including any other material such as cloth or the like, on which it isdesired to maintain a uniform tension when winding.

The speed range valve 91 is used to control the amount of oil enteringthe bellows 78 and adjust the back pres sure which can be varied. Forexample, if the rewind shaft 49 is to turn between 50 and 500 R. P. M.,then the bellows 78 must expand from normal to maximum within this speedrange. If the speed range were from 50 to 1000 R. P. M., then valve 91must be closed a little more than in the previous condition, so that thebellows 78 will expand from normal to maximum for this new speed range.

Fig. 17 illustrates a control system for maintaining a constant let-offtension on a roll of paper or the like, as it is being printed on aprinting press. In the drawing, the gear pump by-pass valve, speed rangevalve, oil reservoir, bellows, rack and pinion, potentiometer andrheostat all operate as described in connection with previous figures.

The roll of paper 102 is mounted on shaft 65 of the device shown in Fig.11. The object is to feed the roll of paper into the press with acertain degree of hold-back tension. As the roll is unwound, the member60 is rotated within the stationary ring 64, secured to the frame 63.The coils 60M on the rotating member are excited and thereforehysteresis is set up in the member 64, which produces a torque whichacts as a drag or brake on the member 60 of shaft 65 connected thereto.As the roll is unwound, the speed of rotation increases. This increasein speed will cause the pump 75 to work faster and expand the bellows78, which, through rack and pinion 92 and 93 will move the contact arm90 of the potentiometer 94, so as to reduce the excitation of coils 60M,thereby maintaining a contant hold-back tension.

It will be understood that the control system shown in Figs. 14-17 aremerely descriptive of the control means that may be used with theinstant invention, and many other forms of control means may be usedthat vary ex- 14 citation current and thereby vary the torque in thedevice. These figures also serve to illustrate some of the practicaluses to which the device can be put.

What is claimed is:

l. In combination with a torque transmitting electrical device having adriving and driven member, one of said members made of high hysteresisloss material and the other of said members having a winding thereof, ashaft connected to said driven member, means for winding a web aboutsaid shaft, a web, a switch having an arm adapted to engage said web tohold said switch in open circuit position when the web is in tension andto move to closed circuit position when said tension is released, acircuit including a source of current, a resistance and said windingwherein varying said resistance will vary the amount of current iiowingthrough said winding and thereby vary the hysteresis loss of said deviceto provide a constant tension on said web, means serially included insaid circuit and controlled by said switch for opening said circuit whensaid switch is opened, a control relay, a circuit controlled by saidrelay and including said source of current, resistance and winding andhaving a variable resistance in circuit therewith, and means controlledby the rotation of said driven shaft for altering the value of saidvariable resistance and thereby changing the magnetism of said device toalter the torque therein to maintain said constant tension on said webindependent of the load applied to said shaft as the web increases insize as wound.

2. The combination as claimed in claim 1, wherein said electrical deviceincludes brake coils adjacent the periphery of that member of the devicemade of high hysteresis loss material, and wherein said brake coils areserially included in a circuit including said switch and said source ofcurrent.

3. The combination as claimed in claim 1, wherein said last meansincludes a fluid operated device connected to said shaft and whereinsaid variable resistance includes an arm operated by said means.

4. The combination as claimed in claim 1, wherein said last meanscontrolled by the rotation of said driven shaft includes a pump, a uidreservoir connected to said pump, an expansible and contractible bellowsconnected to said pump, a by-pass valve between the outlet and inletsides of said pump and a valve between said pump and said bellows.

5. The combination as claimed in claim 1, wherein said variableresistance has a rotary arm, a shaft for said arm, a gear looselymounted on said shaft and connected to said motor, and friction meansbetween said gear and shaft whereby said shaft may be manually adjustedindependently of the position of said gear.

References Cited in the le of this patent UNITED STATES PATENTS 704,574Pintsch July 15, 1902 1,862,267 Honig June 7, 1932 1,982,461 WintherNov. 27, 1934 2,070,447 Morrill Feb. 9, 1937 2,317,290 Mcllvried Apr.20, 1943 2,583,523 Winther Ian. 22, 1952 FOREIGN PATENTS 18,279Australia of 1934 356,945 Great Britain Sept. 17, 1931 OTHER REFERENCESExperimental Elec. Engineering, Karapeto, vol. 1, second edition,published in 1910, by John Wiley and Sons, New York City, page to 195.

